Wax esters functionalized with hydroxyl groups in the alkyl chain of fatty acid are of considerable industrial interest compared with the ordinary wax esters because of their different behaviour including solubility, surface properties and thermal stability. It was reported that these types of waxes have a variety of uses such as plasticizers, mold release agent, emulsifiers and chemical intermediate. Sulphonated wax esters of ricinoleic acid are promising surface active compound.
Currently, the main source of hydroxy fatty acid castor oil and ricinoleic acid (one hydroxylated fatty acid) is the only one used in oleochemical industry to produce various types of waxes. However, the quantities of castor oil (hence ricinoleic acid and its derivatives) available on the market are subjected to considerable fluctuations owing to poor harvests in the main growing areas of Brazil and India. Therefore interest has been focused upon new synthetic methods, which are capable of producing analogue products in large quantities with reasonable cost.
Wax esters are produced by reacting a fatty acid and an alcohol at high temperatures in the presence of catalyst—acidic catalysis or metal catalysis. This high-temperature process can lead to degradation of the esters and undesired side reactions; additionally the resulting energy cost is high. Acidic catalysts are usually time consuming and also give relatively low yields. An acidic catalyst is usually utilized when treating fatty materials containing large amounts of free fatty acids. However, the yields of the fatty esters are usually less than the theoretical amount. Moreover, the high acid contents of the reaction complicate the separation and purification of the fatty esters and the glycerine. Furthermore, the products obtained are often rather poor quality and must undergo various refining steps.
Ghoshray, Bhaftacharyya and Mukesh et al., have produced ricinoleic wax ester from Rhizomucor meihei lipase-catalyzed esterification of ricinoleic acid or alcoholysis of castor oil. While Lang et al. synthesized wax esters of (S)-17hydroxystearic acid and (R)-3-hydroxydecanoic acid with various lipases.